Conventionally, radiodignosis in the medical field means observation of a film image on a viewing screen upon obtaining the film image by radiation exposure. A radiographic image is obtained as an image larger than the actual object size because radiation generated from a tube (radiation generator) is projected on a film through the object.
The distance between two arbitrary points on a film image is conventionally measured by placing a ruler directly on the film. The enlarged magnification must be calculated manually on the basis of the distance from the cassette (film) to the tube.
In recent years, radiographic devices using solid-state image sensing elements have been developed so that digital radiography using a computer is executed. An image obtained by digital radiography is displayed on a monitor such as a CRT or a liquid crystal display and used for diagnosis. In this case, to measure the distance between two points on the image, a scale is superposed on the screen to measure the length of a region to be diagnosed (e.g., Japanese Patent Laid-Open No. 4-54628).
A technique has also been proposed in which the distance from the radiation irradiator to the object and the distance from the object to the radiographic image conversion panel to calculate the radiographic magnification of the object. Accordingly, the distance between two arbitrary points on a radiographed image is accurately measured and displayed (e.g., Japanese Patent Laid-Open No. 11-253429).
When digital X-ray imaging is executed, an image is displayed on a monitor such as a CRT or a liquid crystal display and used for diagnosis. In this case, the distance between two points on the image is measured by using a distance measurement tool or the like as an accessory of the X-ray image display system (e.g., Japanese Patent Laid-Open No. 2000-132667).
In the technique disclosed in Japanese Patent Laid-Open No. 4-54628, the value measured using the scale is the measurement value of an image formed on the sensor which receives radiation that has passed through the object, as described above. Hence, the value is larger by the magnification than the actual object size. Hence, the actual object size cannot be grasped.
In the technique disclosed in Japanese Patent Laid-Open No. 11-253429, only a value corrected by the magnification, i.e., only the actual object size is displayed as the measurement value. Hence, it is difficult to compare the measurement value on the image with the actual object size or grasp the relationship to the magnification.
In the technique disclosed in Japanese Patent Laid-Open No. 2000-132667, the value measured using the distance measurement tool indicates the distance on the sensor which receives X-rays that have passed through the object, as described above. Hence, the value is larger than the actual object size, and the actual object size cannot be obtained. In addition, when only two points on the image are designated, no positions in the direction of depth of the object can be designated. Hence, the distance between two points at different depths cannot be obtained.